1. Field of the invention
Embodiments of the present invention relates to a light emitting diode, and more particularly to a light emitting diode for a liquid crystal display device. Embodiments of the invention are suitable for a wide scope of applications. In particular, embodiments of the invention are suitable for driving a light emitting diode for a liquid crystal display device.
2. Description of the Related Art
Today, electronic display devices are widely used in information driven society. A variety of electronic display devices are being used in various industries. Accordingly, new types of electronic display industry have been and are being developed to satisfy the continually changing needs and requirements of the information driven society.
In general, the electronic display device transmits visual information by converting an electronic signal into an optical signal. For example, the electronic display device may include a light emitting display device, which uses light emission to display the optical signal. In another example, the electronic display device may include a light receiving display device, which uses reflection, scattering, and interference for modulating and displaying the optical signal.
The light emitting display device is called an active display device, examples of which are a cathode ray tube (CRT), a plasma display panel (PDP), an organic electro luminescent display (OELD), and a light emitting diode (LED) display. The light receiving display device is called an inactive display device, examples of which are a liquid crystal display (LCD) and an electro phoretic image display EPID.
The CRT display device has been widely used as a display device for television or computer monitor for a long-time. However, the CRT is heavy, relatively bulky, and has a high power consumption. Recent improvement in semiconductor technology lead to the development of a flat panel display device, which is thin, light and consumes relatively less power. The flat panel display devices being developed include, for example, the LCD, the PDP, and the OELD. The LCD device is of particular interest for use in small electronic devices because it is slim, and thin, and has a low power consumption.
The LCD device includes an LCD panel including a first transparent insulating substrate having a common electrode, a color filter, and a black matrix; a second transparent insulating substrate having a switching element and a pixel electrode; and a liquid crystal material having an anisotropic dielectric constant injected between the first and second transparent insulating substrates. Different voltages are applied to the pixel electrode and the common electrode of the LCD device to adjust a magnitude of an electric field of the liquid crystal material and vary a molecular arrangement of the liquid crystal material. Thus, the amount of light transmitted through the first and second transparent substrates is controlled by the voltage difference between the pixel and common electrodes to display a desired image on the LCD panel.
Because the LCD device is a light receiving display device, it cannot emit the light by itself. Accordingly, a backlight is provided in the back of the LCD panel. The backlight projects light on the LCD panel and maintains a uniform total brightness for the LCD display. The backlight may include a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL) as a light source.
However, the LED is gaining interest as a next generation light source for the backlight because of potential energy saving and quasi-permanent use compared with the CCFL and the EEFL. The use of LED as a backlight source has been so far limited to small-sized LCDs, such as in portable phones. However, recent improvement in the luminance of LEDs expands the use of LEDs as backlight source for mid-size to large LCD devices.
FIG. 1 is a circuit diagram illustrating a device for driving an LED as a light source in a backlight of an LCD device according to the related art. Referring to FIG. 1, the light source for the backlight of the LCD device includes three LED groups D11 to D13, D21 to D23, and D31 to D33. Constant current providing circuits 10, 20, and 30 are provided to power the respective LED groups D11 to D13, D21 to D23, and D31 to D33, respectively. For example, the constant current providing circuit 10 powers the first LED group D11 to D13 The constant current providing circuit 20 powers the second LED group D21 to D23. The constant current providing circuit 30 powers the third LED group D31 to D33. A pulse width modulation signal providing circuit 40 drives the constant current providing circuits 10, 20 and 30. The three groups of LEDs D11 to D13, D21 to D23, and D31 to D33 divide the backlight into three backlight regions, the luminance of which is independently controlled by the respective current providing circuits 10, 20 and 30.
In the related backlight, the constant current providing circuits 10, 20, and 30 should be provided in proportion to the number of the divided backlight regions. Thus, the number of required electronic elements for driving the light emitting diode increases with the number of backlight regions. Hence, the cost of the related art backlight also increases in relation to a number of divided backlight regions. Moreover, the wiring structure of a printed circuit board (PCB) becomes increasingly more complex in relation with the number of backlight regions.